Sprinkler droplet impact angle affects shear stress distribution on soil surface – a case study of a ball-driven sprinkler

Abstract

Droplet shear stress is the main cause of soil erosion under sprinkler irrigation, and the effect of droplet impact angle on the shear stress distribution cannot be ignored. In this study, a ball-driven sprinkler was selected to investigate the radial distributions of droplet impact angles under three operating pressures (0.25, 0.30, and 0.35 MPa) and two nozzle diameters (1.9 and 2.2 mm), which are commonly used in agricultural irrigation. The effect of droplet impact angles on the distances from the sprinkler, droplet impact velocities, and shear stresses were analyzed by a 2DVD instrument. Irrespective of the nozzle diameter or operating pressure, the droplet velocities and impact angles near the sprinkler were distributed at 1.0–5.5 m s−1 and 70–90°, respectively, and the droplet shear stress increased with the distance from the sprinkler. Suitable operating pressure and distance from the sprinkler significantly reduced the droplet shear stress. Although the nozzle diameter had a certain effect on the maximum shear stress, the overall effect was insignificant. We developed the models for the radial distribution of droplet shear stresses, which were in good agreement with the measurement. This study proposes a new method for accurately predicating the soil erosion under sprinkler irrigation. HIGHLIGHTS The soil erosion risk at the end of the spray jet is highly related to droplet shear stress rather than droplet kinetic energy.; Increasing the operating pressure or decreasing the nozzle diameter can effectively reduce the maximum droplet shear stress.; Mathematical models are developed for predicting the radial distribution of droplet shear stress.;

Keywords

• ball-driven sprinkler
• droplet impact angle
• droplet impact velocity
• droplet shear stress
• sprinkler irrigation